The present invention relates to conductive wire for use in supplying an activation signal to a common airbag module that is employed to provide supplemental protection to automobile occupants. The present invention also relates to a cable containing a plurality of conductive wires for carrying a plurality of signals, and to a suppression wire combination that includes a plurality of separate suppression wires.
The airbag inflator assembly art employs the use of pyrotechnic materials for the release of gas at high pressure, nearly simultaneously with vehicle impact during a collision to timely inflate an airbag. The filled airbag then protects the vehicle occupants from substantial harm by providing a cushion to absorb the energy of the momentum transfer. To achieve the timely filling of an airbag, the inflator assembly is designed to utilize a pulse of electrical energy to initiate the rapid combustion of pyrotechnic compounds within the initiator (squib) to produce a high pressure burst of combusting gasses. The intense temperature of these combusting gasses is sufficient to initiate the rapid deposition of a second reservoir of pyrotechnic pellets which yields a large volume of gas sufficient to fully inflate the airbag. An important part of inflator assembly is the detonator or squib. The detonator must be reliable while also capable of integration into the greater assembly unit, bearing in mind the desire for ease of manufacture.
For a detonator to be accepted by the automobile manufacturing industry for the purpose of airbag assembly, the electrical circuit of the detonator must be able to provide protection against inadvertent activation due to intercepting sufficient levels of radiated radio frequency energy (EMI). Thus, appropriate grounding and shielding and utilization of EMI suppression components within a detonator circuit are necessary to ensure that absorption of EMI energy does not inadvertently deploy the air bag. Prevention of inadvertent detonation due to the interception and absorption of EMI is exceedingly important to provide safe vehicle operation.
A connector electrically connects wires that convey an initiation signal, and transfers that signal to the detonator. Inductance is provided in existing systems by positioning separate lumped ferrite blocks or beads within the actual connectors. These ferrite beads occupy significant space within the connectors that contain them, thus causing the connectors to be larger than airbag designers would prefer. Moreover, the connectors are complex, increasing size and manufacturing expense, while arguably reducing overall reliability. There is great pressure from vehicle manufacturers to reduce the size and manufacturing expense of these connectors while improving performance and reliability.
The utalization of inductance to limit the emission and absorption of EMI radiation is also desirable for combinations of multiple suppression wires, and for wire cables that carry a plurality of signals. The need for suppression of EMI radiation and absorption (RFI) is particularly present in cables that carry both electrical power as well as data signals. For example, cables that carry electric power and data signals to a remote sensor have employed the use of some type of metallic braid or shield within the outer cable jacket to enhance suppression of either internally or externally generated RFI. Other cables have additional insulating material packed around and between the conductive wiring that shields EMI radiation. Addition of these components requires additional cost and production time and adds unwanted complexity to the cable construction. It is therefore desirable to provide a suppression wire combination, as well as a suppression cable, where each does not require the addition of extra suppression materials acting as shields or insulating fillers.
A suppression wire for a detonation circuit of an airbag according to the present invention includes a stranded copper conductor, a layer of ferrite filled polymer extruded around the stranded copper conductor, and an insulation layer that is preferably annularly extruded around and directly over the ferrite filled polymer. One end of the self-suppression pair of wires is connected to an ignition signal generator, and the other end of the pair is connected to a detonator, the detonation of which results in rapid airbag inflation.
The stranded copper conductor is gauge sized ranging between sixteen and twenty-eight gauge in a preferred embodiment of the invention. Furthermore, the polymer that has ferrite dispersed therein may be selected from such polymers as polyvinyl chloride, cross-link polyethylene, a polytetrafluoroethylene (PTFE) polymer such as Teflon(copyright), silicone, an ethylene propylene diene polymer, fluorinated ethylene propylene terpolymer rubber, and a polyvinylidene (PVDF) polymer such as Kynar(copyright). One could also utilize various formulations of ferrite. The ferrite is disposed within the polymer in the form of a fine powder with an average particle size typically between one micrometer and two hundred micrometers. The chemical composition of the ferrite determines the degree of suppression effect (impedance) imparted to the conductor overlaid with a ferrite filled polymer and also the frequency range over which the impedance is preferentially imposed on the conductor. For example, ferrites belonging to the manganese zinc class preferentially impose inductance and suppression at low frequencies (less than 30 megahertz). Also, nickel zinc type ferrites impart enhanced impedance at higher frequencies (25 through 200 megahertz). These ferrite compound families can be compounded with any of the above polymers to achieve the preferential enhanced suppression impedance at frequency ranges requiring enhanced suppression.
The present invention also involves a method of manufacturing an ignition signal system, which includes the steps of providing the above-described suppression wire, connecting one end of the suppression wire to an ignition signal generator, and connecting the other end of to a detonator, the detonation of which results in vehicle airbag inflation.
In a second embodiment of the invention, a suppression wire cable for operation of an electronic device according to the present invention includes a plurality of suppression wires, each of which includes a stranded copper conductor. A layer of ferrite filled polymer is preferably extruded around and directly on each stranded copper conductor. An insulation layer is preferably extruded around and directly on the ferrite filled polymer. A protection jacket that comprises a polymer material is provided as an outer layer. The plurality of suppression wires are preferably in a twisting formation, and the outer protection jacket serves to maintain the formation.
Because there are a plurality of suppression wires in the cable of the present invention, both data signals and electrical power can be channeled through the cable. Also, the ferrite filled polymer and the outer protection jacket each include a polymer selected from polyvinyl chloride, cross-link polyethylene, a PTFE polymer, silicone, an ethylene propylene diene polymer, fluorinated ethylene propylene terpolymer rubber, and a PVDF polymer.
A method of manufacturing a suppression wire cable according to the present invention includes the steps of providing a plurality of the above described suppression wires, preferably forming the suppression wires in a twisting formation, and surrounding the suppression wires with the above-described outer protection jacket.
A third embodiment of the present invention also includes a suppression wire combination, which includes a) a first suppression wire, including a first stranded copper conductor, a first layer of ferrite filled polymer, extruded around the first stranded copper conductor, and a first insulation layer, extruded around the first ferrite filled polymer; b) a second suppression wire, identical in its construction as the first suppression wire, and c) a connecting rib, connecting the first and second insulation layers. The first insulation layer, second insulation layer, and connecting rib are integrally molded.
According to the third embodiment of the invention, additional suppression wires, each being identical to the first and second suppression wires, are provided so that the insulation layers, and connecting ribs separating them are all integrally molded, and all of the suppression wires are disposed in a flat row.